Rename project_eigenvectors to rotate_to_physical_auxiliary_basis with improved documentation

[Copilot]

Renamed project_eigenvectors in dyson/util/linalg.py to better reflect its purpose: constructing a biorthonormal basis spanning physical (Dyson orbitals) and auxiliary (null space) spaces, then rotating eigenvectors into that basis.

Changes

• Function rename: project_eigenvectors → rotate_to_physical_auxiliary_basis

  • Follows naming pattern of similar functions (rotate_subspace, set_subspace)
  • Explicitly describes the transformation and target basis

• Enhanced docstring:

  • Step-by-step procedure for Hermitian vs non-Hermitian cases
  • Shape specifications for all parameters and return values
  • Mathematical context: physical space (bra/ket Dyson orbitals) vs auxiliary space (null space of projector)

• Updated call sites: spectral.py, exact.py, davidson.py, util/__init__.py

Example

# Hermitian system - constructs rotation from physical+auxiliary basis
eigvecs = util.rotate_to_physical_auxiliary_basis(
    eigvecs, bra, ket=None
)

# Non-Hermitian system - biorthonormalizes before rotating
eigvecs = util.rotate_to_physical_auxiliary_basis(
    eigvecs, bra, ket
)

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